1. Field of the Invention
This invention generally relates to system gain measurement techniques and, more particularly, to a system and method for measuring amplifier gain in a digital network receiver front-end.
2. Description of the Related Art
FIG. 1 is a schematic diagram of a conventional digital receiver front-end (prior art). The digital receiver is designed to receive a wide dynamic range input signal. Even if the format of the signal is digital, the wide dynamic range of the input signal gives it characteristics of an analog signal. The purpose of the amplifier is to supply an amplified output signal to an interfacing comparator. If the amplifier gain is too small, the signal may be too small to properly trigger the comparator. Too much gain may result in an amplified signal becoming saturated or distorted, so that it will also be unable to properly trigger the comparator. Either way, improper amplification can result in a bit of information being misinterpreted.
Due to fabrication process tolerances, the exact gain of the amplifier can vary. Therefore, the amplifier gain is monitored. If the signal strength is small, the amplifier gain is increased to optimize the drive level to the interfacing comparator. If the input signal strength is too large, the amplifier gain is minimized to provide the optimal drive to the comparator. However, this approach requires that an integrated circuit (IC) pin be dedicated to monitoring the amplifier output. As the size of ICs decreases, and their functionality increases, it becomes difficult to justify the dedication of a pin to any particular purpose.
Alternately, the receiver front-end may include an automatic gain control (AGC) circuit (not shown). However, AGC circuitry is complicated and can be difficult to calibrate. In other aspects (not shown), the amplifier gain is not monitored, but set assuming a predetermined gain and input signal amplitude. The simplicity of this approach is offset by the degradation of network performance in situations where the actual gain differs from the assumed gain.
It would be advantageous if the gain of a digital receiver front-end amplifier could be determined without having to directly monitor the amplifier output via a dedicated IC pin.
It would be advantageous if the gain of a digital receiver front-end amplifier could be optimized by analyzing the output of the interfacing comparator circuit.
The present invention provides a system and method for determining the gain of a digital receiver front-end amplifier, without having to dedicate an IC pin for directly monitoring the amplifier output. The present invention simplifies the design of a digital receiver network, without degrading receiver sensitivity.
Accordingly, a method is provided for measuring amplifier gain in a digital network. The method comprises: accepting a digital input signal (Vin); amplifying the input signal; comparing the amplified signal to dc thresholds; measuring output errors; and, calculating the amplifier gain in response to the thresholds.
More specifically, accepting a digital input signal includes accepting an input signal having a predetermined (or measured) amplitude. Comparing the amplified signal to dc thresholds includes comparing the amplified signal to a low threshold and a high threshold. Measuring errors includes measuring a predetermined error condition in response to the high threshold and the low threshold. Then, calculating the amplifier gain in response to the thresholds includes calculating the amplifier gain in response to the high threshold, the low threshold, and the input signal amplitude.
Additional details of the above-described method, and a system for measuring amplifier gain in a digital network are provided below.